MI2011: Horizontal DNA Transfer

Question 1

Conjugation

Answer 1

The one way transfer of DNA from one live bacterium to another via a pilus or chemical signalling, drawing the bacteria together and resulting in the spread of plasmid

Question 2

Transformation

Answer 2

uptake of free DNA, in the form of plasmids or DNA released from dead bacteria closely related to the bacteria that take it up

Question 3

Transduction

Answer 3

bacteriophage pick up genetic material from one bacterial cells and deposit it in another

Question 4

What are the 5 main characteristics encoded by plasmid genes?

Answer 4

1. Antibiotic Resistance (R)
2. Colicin genes (Col)
3. Degradative plasmids
4. Virulence plasmids
5. Conjugative Plasmids (F+)

Question 5

What are the characteristics of the donor cell in conjugation of plasmids

Answer 5

1. A plasmid carrying genetic information required for promoting DNA transfer
2. Pilli

Question 6

What is the F factor?

Answer 6

A set of tra genes in the plasmid that controls and promotes the DNA transfer from the donor cell

Question 7

What components make up the tra system of the plasmid?

Answer 7

• origin of transfer
• origin of replication
• replication genes
• transfer of tra genes

Question 8

Describe the process of conjugation in F plasmids?

Answer 8

See Word Document

Question 9

Is the process of transformation complementarily dependent?

Answer 9

Yes. The uptake of free DNA is dependent upon the level of competence of recipient cells. Fully competent cells have modified cell walls and specific receptor sites on the plasma membrane that will bind free DNA.

Question 10

Describe the process in which bacteriophage infect the host cell

Answer 10

Bacteriophage are viruses that infect bacteria and use their hosts factors for replication. They infect bacteria by attaching to specific receptors on the cell surface and injecting nucleic acid into the cell.

Question 11

Lytic

Answer 11

No integration, replication by making progeny phage and lysing cell for release to infect (horizontal transfer)

Question 12

Lysogenic

Answer 12

Integration into host genome, replication along with chromosomal DNA (vertical transfer)

Question 13

Describe Lysogenic Cycle

Answer 13

1. DNA molecule injected
2. Brief transcription period where a repressor and an integrase are transcribed
3. Repressor turns off subsequent transcription of viral DNA
4. Integration into host genome
5. Replication along with host

Question 14

Generalised Transduction

Answer 14

• transfers fragments of the host DNA only
• only contains host bacterial DNA, NOT phage DNA
• transducing particles infect recipient cell
• success of transducing phage is dependent on ability to integrate into a new host

Question 15

What is the result of generalised transduction?

Answer 15

Recombination can occur, producing a recombinant cell with a genotype different from both the donor and recipient cells.

Question 16

Specialised Transduction

Answer 16

• occurs with lysogenic phages
• transduction of host DNA which flanks the prophage
• results from excision error of phage DNA upon lytic trigger
• results in loss of some phage genes

Question 17

Transposition

Answer 17

the ability of a genetic sequence to move from one location to another

Question 18

Transposons

Answer 18

the transposable element in transposition

- do not exist independently, must shift between DNA

Question 19

Transposition if mediated by an enzyme coded for by the transposable genetic element. This enzyme is called?

Answer 19

Transposase

Question 20

A simple form of transposition that only encodes for transposase

Answer 20

Insertion sequences

Question 21

A more complex form of transposition that encodes for several genes

Answer 21

composite transposons

Question 22

What are the two mechanisms of transposition

Answer 22

Conservative and Replicative

Question 23

Define conservative transposition

Answer 23

Transposon is cut out of DNA and inserted into new location.

Question 24

Define replicative transposition

Answer 24

Transposon is replicated, one copy remains at original location, other is moved to new location. Donor DNA undamaged.

Question 25

Insertion sequences

Answer 25

inverted repeats at ends of DNA sequence

Question 26

What are potential consequences of insertion sequences

Answer 26

• mutation
• plasmid insertion into chromosomes
• gene expression

Question 27

Composite transposons

Answer 27

carry one or more other genes, in addition to those which are essential for transposition.
- flanked by insertion sequences